Fuel pump whine

[ChrisMBauto]

Need some help, I have been fighting my Volvo penta 5.0 Gi to run. My problem is this, it started with losing idle and hearing the infamous fuel pump whine, replaced the FP, and when started same problem, had marine mechanic look at it and found the ECU was bad, replace the control module, started the boat and was able to get it to stay running at idle, BUT the fuel pump is whining again, so I replaced the fuel pump under warranty, when I installed the new fuel pump and primed the system,and started the boat, right out the gate the fuel pump is whining. Shut motor off and started looking for restriction in the pick up tube, fuel hose from tank to pump, and even fuel lines from fuel pump to throttle body. Found no blockage. Only thing I notice, was the check valve at the fuel pick up was not a check valve, just a straight flow. Allowing fuel to bleed back into the tank. Replaced it with proper check valve. I wondering if anyone has seen this problem before, and can guide me in the right direction for the repair.....